3 Experimental Studies Intervention Studies The investigator himself

3 - Experimental Studies (Intervention Studies): The investigator himself allocates the exposure then follows subjects for the subsequent development of disease.

3 - Experimental Studies (Intervention Studies): Characteristics:

Types of experimental studies: �Preventive type: �Therapeutic type:

Limitations of experimental studies: Ethical concerns …. .

Limitations of experimental studies: Difficult to find large number of individuals willing to forego a treatment or practice believed to be beneficial for the duration of a trial Cost;

Selection of a study population; The experimental population; Reference population;

MEASURMENTS OF RISK �Realative Risk(RR): �*It is an estimation of the association between exposure and disease.

Incidence rate among exposed RR=---------------------- Incidence rate among non exposed

Interpreting RR of a disease: *If RR= 1 Risk in exposed equal to risk in unexposed (no association). *If RR> 1 Risk in exposed is greater than the risk in unexposed (positive association, possibly causal). *If RR < 1 Risk in exposed is less than the risk in unexposed (negative association, possibly protective)

Attributable Risk (AR): It indicates how much of the disease is attributed to that particular risk factor. . . or the other way round. . . how much those of the non –exposed will develop or get the disease if they are exposed to the risk factor

Example: In a study of two toothpastes, 10 out of 100 caries-free children using a new toothpaste (exposure) develop caries after 1 year. In another group of 100 caries-free children using a standard toothpaste, 25 develop caries

�Example: In a prospective study of the risk of alcohol consumption on developing TB � ---+VE----- -VE --- Total �Alcoholic 40 10 50 �Non-Alcoh 10 90 100 �Total 50 100 150

Example: A study on smoking had shown the followings: -